Context guided retrieval

This paper presents a hierarchical case representation that uses a context guided retrieval method The performance of this method is compared to that of a simple flat file representation using standard nearest neighbour retrieval. The data presented in this paper is more extensive than that presented in an earlier paper by the same authors. The estimation of the construction costs of light industrial warehouse buildings is used as the test domain. Each case in the system comprises approximately 400 features. These are structured into a hierarchical case representation that holds more general contextual features at its top and specific building elements at its leaves. A modified nearest neighbour retrieval algorithm is used that is guided by contextual similarity. Problems are decomposed into sub-problems and solutions recomposed into a final solution. The comparative results show that the context guided retrieval method using the hierarchical case representation is significantly more accurate than the simpler flat file representation and standard nearest neighbour retrieval

Manual pressing of nannochloropsis oculata dried biomass for enhanced lipid extraction

Microalgae offer significant potential to produce high value products and biofuels, whilst simultaneously being used to bio-remediate water or capture carbon dioxide (CO2). Microalgal cell disruption processes are often necessary to increase lipid extraction from microalgae before conventional solvent extraction processes are used to isolate lipids. The extracted lipids can be processed to produce biofuels. The combinations of hydraulic pressing with liquid nitrogen (LN2) treatment were applied to samples of dried Nannochloropsis oculata in the presented study to enhance the cellular destruction and lipid yields. The results indicated higher lipid extraction with LN2 treatment (0.159 g/g dry algae) compared to the LN2 untreated samples (0.070 g/g dry algae). The corresponding cell disruptions were found to be seventy-eight and fifty percent, respectively, at the same 10 bar (145 psi) pressure level. The control sample (without any treatment) lipid yield was 0.006 g/g dry algae, while the lipid yield varied between 0.192-0.213 g/g dry algae with LN2 treated biomass with pressure loadings of 70-100 bar (1015-1450 psi) and with a corresponding cell disruption of 93-98 percent. The presence of palmitate, oleate and linoleate found in the fatty acid methyl ester composition of the extracted lipids, shows a favourable profile to produce biodiesel

Fast magnetic reconnection via jets and current microsheets

Numerical simulations of highly nonlinear magnetic reconnection provide evidence of ultrathin current microsheets. These small-scale sheets are formed by strong exhaust jets from a primary large-scale current layer. The overall size of the secondary microsheet is determined by the thickness of the primary sheet. Preliminary scalings show that the thickness of the microsheet varies linearly with the plasma resistivity. This scaling suggests that microsheets may provide fast reconnection sites in magnetically complex plasmas such as the solar corona and planetary magnetospheres

Dynamic planar magnetic reconnection solutions for incompressible plasmas

The planar magnetic reconnection problem for viscous, resistive plasmas is addressed. We show that solutions can be developed by superposing transient nonlinear disturbances onto quiescent “background” fields. The disturbance fields are unrestricted in form, but the spatial part of the background field must satisfy ∇2K= -λK. This decomposition allows previous analytic reconnection solutions, based on one-dimensional disturbance fields of “plane wave” form, to be recovered as special cases. However, we point out that planar disturbance fields must be fully two-dimensional to avoid the pressure problem associated with analytic merging models, that is, to avoid unbounded current sheet pressures in the limit of small plasma resistivities. The details of the reconnection problem are then illustrated using cellular background field simulations in doubly periodic geometries. The flux pile-up rate is shown to saturate when the pressure of the current sheet exceeds the hydromagnetic pressure of the background field. Although the presaturation regime is well described by one-dimensional current sheet theory, the nonlinear postsaturation regime remains poorly understood. Preliminary evidence suggests that, although after saturation the early evolution of the field can be described by slow Sweet-Parker scalings, the first implosion no longer provides the bulk of the energy release

Construction and Operation of a Two-place Diver's Sled

Fisheries gear researchers have employed scuba diver-operated sleds to evaluate towed fishing systems since the early 1950's. One of the earliest sled designs was a converted Stokes litter in which two divers sat tandem with the forward diver operating the diving controls (Sand, 1956). The litter was relatively easy to maneuver and provided a comfortable platform for observing operational fishing gear. However, the use of underwater photographic equipment to document gear performance was difficult due to the limited mobility of the observer-cameraman

The impact of small-scale turbulence on laminar magnetic reconnection

Initial states in incompressible two-dimensional magnetohydrodynamics that are known to lead to strong current sheets and (laminar) magnetic reconnection are modified by the addition of small-scale turbulent perturbations of various energies. The evolution of these states is computed with the aim of ascertaining the influence of the turbulence on the underlying laminar solution. Two main questions are addressed here: (1) What effect does small-scale turbulence have on the energy dissipation rate of the underlying solution? (2) What is the threshold turbulent perturbation level above which the original laminar reconnective dynamics is no longer recognizable. The simulations show that while the laminar dynamics persist the dissipation rates are largely unaffected by the turbulence, other than modest increases attributable to the additional small length scales present in the new initial condition. The solutions themselves are also remarkably insensitive to small-scale turbulent perturbations unless the perturbations are large enough to undermine the integrity of the underlying cellular flow pattern. Indeed, even initial states that lead to the evolution of small-scale microscopic sheets can survive the addition of modest turbulence. The role of a large-scale organizing background magnetic field is also addressed

The power output of spine and fan magnetic reconnection solutions

The ability of three-dimensional magnetic “spine” and “fan” reconnection solutions to provide flarelike energy release is discussed. It is pointed out, on the basis of exact analytic solutions, that fast dissipation is possible only if the hydromagnetic pressure in the reconnection region becomes unbounded in the limit of small plasma resistivities. The implication is that some “saturation” of the power output is inevitable for realistic coronal plasmas. Estimates of the saturated power, based on limiting the flux pileup in the field, suggest that the geometry of the spine reconnection mechanism precludes significant flare energy release. However, the current sheet structures involved in fan reconnection seem able to release sufficient magnetic energy fast enough to account for modest flares, even under the conservative assumption of classical plasma resistivities

Opinn aðgangur að fræðigreinum

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenHEFUR þú einhvern tíma gúglað eitthvað á netinu og fundið fræðigrein um nákvæmlega það sem þú varst að leita að – en því miður er fræðigreinin læst og þú getur ekki lesið hana nema þú sért með áskrift eða borgir fyrir hana? Því miður hafa margir lent í þessu en tímarnir eru smám saman að breytast og lokaður aðgangur verður sjaldgæfari með degi hverjum. Á netinu er opinn aðgangur að æ fleiri tímaritum og greinar þeirra öllum aðgengilegar án endurgjalds. Öflug alþjóðleg hreyfing fræðimanna og bókasafnsfræðinga hefur breytt útgáfulandslaginu griðarlega á síðustu fimm til tíu árum (sjá www.earlham.edu/~peters/fos) og í dag, þriðjudaginn 14. október, er alþjóðlegur dagur opins aðgangs (sjá openaccessday.org)

Exact models for hall current reconnection with axial guide fields

This paper employs an analytic reconnection model to investigate the conditions under which Hall currents can influence reconnection and Ohmic dissipation rates. It is first noted that time dependent magnetohydrodynamic systems can be analyzed by decomposing the magnetic and velocity fields into guide field and reconnecting field components. A formally exact solution shows that Hall currents can speed up or slow down the reconnection rate depending on the strength and orientation of the axial guide field. In particular, merging solutions are developed in which the axial guide field is the dominant driver of the reconnection. The extent to which Hall currents can alleviate the buildup of back pressures in flux pile-up reconnection models is also examined. The analysis shows that, although enhancements of the merging rate can be expected under certain conditions, it is unlikely that Hall currents can completely undo the fundamental pressure limitations associated with flux pile-up reconnection